1. Field of the Invention
The present invention relates to a vibration actuator and, more particularly, to a vibration actuator which utilizes degeneracy between an extensional vibration or non-axisymmetric vibration and a bending vibration.
2. Related Background Art
Conventionally, a first type of vibration actuator generates a travelling vibration wave in a ring-shaped elastic member by exciting electro-mechanical converting elements, thereby driving a movable member (rotor) as a relative moving member which is in press contact with the elastic member.
In a second type, i.e., a linear vibration actuator, a vibration applying electro-mechanical converting element is disposed on one end portion of a rod-shaped elastic member, and a vibration absorbing electro-mechanical converting element for absorbing reflection of a travelling wave is disposed on the other end portion. With this arrangement, a travelling wave that propagates from one end to the other end of the elastic member is generated, thereby driving a movable member which is in press contact with the elastic member.
The first type of vibration actuator is often assembled in, e.g., a lens barrel of a camera, and is used for driving an AF lens upon rotation of the movable member.
An image blur prevention device for correcting an image blur by moving a portion of a photographing optical system in a plane substantially perpendicular to the optical axis has been proposed. However, the first type of actuator cannot be applied to this device since its driving direction does not match. On the other hand, the second type of actuator cannot be easily assembled in a cylindrical lens barrel, and makes the device bulky to attain driving operations in two directions, i.e., the X- and Y-directions in the plane perpendicular to the optical axis.
When an electromagnetic motor, which has high-speed, low-torque features, is to be utilized, a gear train is normally required to assure a high output torque. Furthermore, when an object to be driven is to be moved in two directions in a plane, two, independent pairs of electromagnetic motors and gear trains are required to drive the object to be driven in the respective directions. For this reason, the device is made bulky and its weight increases. In addition, a decrease in response, generation of noise, and the like occur due to backlash or the like as an inevitable problem of the gear train.